bug#66224: [PATCH] Add optional PREDICATE argument to read-directory-name

[Joseph Turner via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Tue, 26 Sep 2023 18:16:40 -0700
>> From:  Joseph Turner via "Bug reports for GNU Emacs,
>>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>>
>> This patch makes read-directory-name accept an optional PREDICATE arg
>> so it can be used like read-file-name.
>
> Any rationale?

Mainly code clarity. If you want to prompt for a certain type of
directory, then IMO the intent is more clear like this:

(read-directory-name "Prompt: " "~/" nil nil nil #'my/predicate)

than like this:

(read-file-name "Prompt: " "~/" nil nil nil
                (lambda (filename)
                  (and (funcall #'file-directory-p filename)
                       (funcall #'my/predicate filename))))

Also, I think that it would follow the principle of least suprise to
have read-file-name and read-directory-name accept the same args.

>> @@ -1719,7 +1719,9 @@ combining @var{directory} (or the current buffer's default directory
>>  if @var{directory} is @code{nil}) and @var{initial}.  If both
>>  @var{default} and @var{initial} are @code{nil}, this function uses
>>  @var{directory} as substitute default, or the current buffer's default
>> -directory if @var{directory} is @code{nil}.
>> +directory if @var{directory} is @code{nil}.  The union of sixth arg
>> +@code{predicate} and @code{file-directory-p} is passed as the
>
> This should be elaborated: what is meant by "the union of sixth arg
> and 'file-directory-p'"?
>
>> +@code{predicate} argument to ‘read-file-name’.
>                                 ^^^^^^^^^^^^^^^^
> That should be @code{read-file-name}
>
>> +** 'read-directory-name' now accepts an optional PREDICATE argument.
>> +The union of sixth arg PREDICATE and 'file-directory-p' is passed
>> +as the PREDICATE argument to 'read-file-name'.
>
> Likewise here, regarding the "union" part.
>
> Also, since you submit the patch for the manual, this NEWS entry
> should be marked with "+++".
>
>>  Fifth arg INITIAL specifies text to start with.
>>  DIR should be an absolute directory name.  It defaults to
>> -the value of `default-directory'."
>> +the value of `default-directory'.
>> +The union of sixth arg PREDICATE and `file-directory-p' is passed
>> +as the PREDICATE argument to `read-file-name'."
>
> The "union" part again.

Thanks for the review!! Please see attached patch.

Best,

Joseph


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From 1c7581914c1b446ea17692d425a4605d915fa7ef Mon Sep 17 00:00:00 2001
From: Joseph Turner <joseph@breatheoutbreathe.in>
Date: Thu, 28 Sep 2023 20:27:47 -0700
Subject: [PATCH] Add optional PREDICATE argument to read-directory-name

* lisp/files.el (read-directory-name): Add optional PREDICATE arg.
* doc/lispref/minibuf.texi (Reading File Names): Document change.
* etc/NEWS: Note change.
---
 doc/lispref/minibuf.texi |  8 ++++++--
 etc/NEWS                 |  7 +++++++
 lisp/files.el            | 14 +++++++++++---
 3 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/doc/lispref/minibuf.texi b/doc/lispref/minibuf.texi
index 620c58ec6e9..eb344595ae3 100644
--- a/doc/lispref/minibuf.texi
+++ b/doc/lispref/minibuf.texi
@@ -1709,7 +1709,7 @@ If this variable is non-@code{nil}, @code{read-file-name} ignores case
 when performing completion.
 @end defopt
 
-@defun read-directory-name prompt &optional directory default require-match initial
+@defun read-directory-name prompt &optional directory default require-match initial predicate
 This function is like @code{read-file-name} but allows only directory
 names as completion alternatives.
 
@@ -1719,7 +1719,11 @@ combining @var{directory} (or the current buffer's default directory
 if @var{directory} is @code{nil}) and @var{initial}.  If both
 @var{default} and @var{initial} are @code{nil}, this function uses
 @var{directory} as substitute default, or the current buffer's default
-directory if @var{directory} is @code{nil}.
+directory if @var{directory} is @code{nil}.  Sixth arg
+@code{predicate}, if non-nil, should be a function of one argument;
+then a file name is considered an acceptable completion alternative if
+both @code{file-directory-p} and @code{predicate} return non-nil with
+the file name argument.
 @end defun
 
 @defopt insert-default-directory
diff --git a/etc/NEWS b/etc/NEWS
index 1b3532b5657..a5a41d6546f 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -3541,6 +3541,13 @@ This function is called to see whether what the user has typed is a
 match.  This is also available from functions that call
 'completing-read', like 'read-file-name'.
 
++++
+** 'read-directory-name' now accepts an optional PREDICATE argument.
+Sixth arg PREDICATE, if non-nil, should be a function of one argument;
+then a file name is considered an acceptable completion alternative if
+both `file-directory-p' and PREDICATE return non-nil with the file
+name argument.
+
 ** 'posn-col-row' can now give position data based on windows.
 Previously, it reported data only based on the frame.
 
diff --git a/lisp/files.el b/lisp/files.el
index b72f141c0ee..1663f1e2d71 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -807,7 +807,7 @@ See Info node `(elisp)Standard File Names' for more details."
     (dos-convert-standard-filename filename))
    (t filename)))
 
-(defun read-directory-name (prompt &optional dir default-dirname mustmatch initial)
+(defun read-directory-name (prompt &optional dir default-dirname mustmatch initial predicate)
   "Read directory name, prompting with PROMPT and completing in directory DIR.
 Value is not expanded---you must call `expand-file-name' yourself.
 Default name to DEFAULT-DIRNAME if user exits with the same
@@ -821,14 +821,22 @@ Fourth arg MUSTMATCH non-nil means require existing directory's name.
  Non-nil and non-t means also require confirmation after completion.
 Fifth arg INITIAL specifies text to start with.
 DIR should be an absolute directory name.  It defaults to
-the value of `default-directory'."
+the value of `default-directory'.
+Sixth arg PREDICATE, if non-nil, should be a function of one
+argument; then a file name is considered an acceptable completion
+alternative if both `file-directory-p' and PREDICATE return
+non-nil with the file name argument."
   (unless dir
     (setq dir default-directory))
   (read-file-name prompt dir (or default-dirname
 				 (if initial (expand-file-name initial dir)
 				   dir))
 		  mustmatch initial
-		  'file-directory-p))
+                  (if predicate
+                      (lambda (filename)
+                        (and (file-directory-p filename)
+                             (funcall predicate filename)))
+                    #'file-directory-p)))
 
 \f
 (defun pwd (&optional insert)
-- 
2.41.0